Apparatus for the manufacture of thin-walled shaped articles of thermoplastic material

ABSTRACT

Thin-walled articles of thermoplastic material are formed in a continuous apparatus starting with heating and extruding granular thermoplastic raw material in the form of a continuous web which is immediately stabilized by rapid cooling of its opposite surfaces and the stabilized web wherein the material sandwiched between the precooled outer surface layers remains at or near extrusion temperature is fed into a thermal forming station wherein shaping tools form the articles in the web without the need for further heating of the web. Adjustments are provided for correlating the cooling action to different materials and web feed rates, for varying the web feed rates and increments, and for varying the shaping tool movements to adapt for different materials and sizes of articles. After the formed articles are separated from the web the web residue is fed back to be mixed with incoming raw material at the extrusion station.

This is a continuation-in-part of copending application Ser. No. 408,083filed Oct. 19, 1973 now abandoned for Method and Apparatus for FormingThin-Walled Articles From Thermoplastic Material.

This invention relates to a manufacture of thin-walled articles such ascups, plates and like containers of synthetic thermoplastic material,and particularly to special method steps and apparatus for making thearticles.

In its preferred embodiments the invention will be disclosed asincorporated in an in-line thermal forming method and apparatus, whereina thermoplastic material, preferably of the granular kind, isplasticized by heating and compression and cast into a plastic web asfrom a fish-tail nozzle, or cast into several plastic webs fromdifferent fish-tail nozzles, the several plastic webs being superposedand united immediately into a composite web. The web is rapidly cooledat its opposite exposed surfaces in a stabilizing station so that asandwich-like condition is obtained, wherein the two surface layers ofthe web will become more solidified and supportive while the core orinternal layer or layers will remain highly plastic and paste-like orfluid. Despite stabilization and cooling, the outer layers remain warmand soft enough to be deformed by die or other tool action. Thestabilized web is subsequently subjected to a thermal forming processwherein the outer layers of the web are deformed to shapes correspondingto die contours while the still hot fluid internal plastic material isdistributed between the shaped outer layers.

BACKGROUND OF THE INVENTION

In most known thermal forming methods (see U.S. Pat. No. 3,115,677), apreviously manufactured and completely cooled and stored thermoplasticweb is heated, usually by infra-red radiation, prior to the thermalshaping on one or both surfaces, to a forming temperature. Thermoplasticmaterials being poor heat conductors however, the web must be raised tovery high and usually uncontrollable temperatures at the surface orsurfaces in order to supply sufficient heat to raise the web core to thedesired temperature. If relatively thick webs, for example websexceeding 1 mm in thicknesses, are to be formed to articles,considerable time is required for heating the web through the surfaces.Furthermore, considerable damage may be caused at the web surfaces,whether thick or thin webs, because of excessively high temperatures andespecially because of possible oxidation at those high temperatures, sothat thermoplastic articles so made may be degraded at least at theouter surfaces.

In-line thermal forming methods are known (German Auslegeschrift1,165,241; U.S. Pat. No. 2,891,980), wherein a thin thermoplastic web iscontinuously cast from an extruder followed by a fish-tail nozzle and isfed to a device converting the continuous advance into a stepwiseadvance, whence the web will be brought to negative (female) dies in athermal shaping machine. In these known methods, the web is set fortemperatures as low as possible during casting from the nozzle so thatit may be immediately fed to the advance converter. The heat supplied tothe web during extrusion is kept so low that it usually will not sufficeor be retained for the ensuing thermal forming, and so additionalheaters acting on the web surface are provided which may result in theabove described drawbacks with respect to web surface.

Another example of prior art methods and apparatus involving successiveweb forming and thermal shaping is disclosed in U.S. Pat. No. 2,697,328.

OBJECTS AND ADVANTAGES OF THE INVENTION

It is a major object of the invention to provide novel apparatus formanufacturing articles from thermoplastic material wherein an extrudedhot plastic web is immediately stabilized by being cooled along itsopposite surfaces to provide along those surfaces shell or supportiveouter layers that are warm and soft enough to be deformable bysubsequent shaping die action while the thermoplastic materialinternally of those layers remains sufficiently hot to retain plasticityand be capable of redistribution between the outer layers during dieaction.

Another object of the invention is to provide novel apparatus for themanufacture of articles from thermoplastic material, wherein thematerial is compressed and heated in an extruder to liquefaction and iscast into a hot plastic web (or several hot plastic web components maybe cast and superposed to form a composite web) and the web immediatelyupon leaving the extruder nozzle or nozzles will be stabilized whilestill in the hot plastic state by being so cooled at both surfaces thatthe thermoplastic material at those surfaces will form supportive layersthat are deformable even though stable, while the material interiorly ofthose layers essentially remains at the extrusion temperature and in thefluid or plastic state, and then subjecting the web so stabilized to athermal forming operation.

A further object of the invention is to provide novel apparatus forcontrollably cooling the opposed surfaces of a freshly formed hotplastic web. Pursuant to this object adjustment may be provided forselectively regulating the degree of cooling.

Another object of the invention is to provide in the foregoing novelapparatus providing an additional sequence between surface cooling ofthe web and shaping the web, whereby the temperature at the web surfacesis made uniform over section of the web to be subjected to shaping in asubsequent operation. Pursuant to this object novel apparatus iscontemplated wherein the surface temperature distribution over the websection may be accomplished by reflectors proportionately reflectingheat radiated from the hot plastic web, and/or heated air circulationsystems effective at the web surfaces.

A further object of the invention is to form a composite web fromthermoplastic materials, where the material layer or layers at one orboth surfaces of the web may be of different properties than at thecore. For example, the web may be butadiene-rubber modified polystyreneat the surface or surfaces, that is, impact-proof polystyrene, whilebeing standard polystyrene at the core.

Another object of the invention is to form a composite web fromthermoplastic materials, the material at the surface or surfaces being apolyolefin, for example polypropylene or polyethylene, while thematerial at the core will be a polystyrene or a polystyrene reacted withbutadiene-rubber. An appreciably more marked surface sheen may beachieved in this manner, with improved relief shaping and considerablyincreased water vapor sealing in the formed articles.

A further object of the invention is to form a composite web fromthermoplastic materials, the material being a polycarbonate at thesurfaces and a standard polystyrene, or one modified with animpact-proof butadiene-rubber, at the core. Formed articles may beeconomically made in such manner that will remain rigid,temperature-resistant and glossy to a temperature range of 130°-135° C.

Another object of the invention is to make a composite web fromthermoplastic materials the outer layers of which are a standardpolystyrene or polystyrene modified with butadiene-rubber, and of ashaping temperature in the range of 130°-140° C, and the material of theweb core being a poly-alpha-methyl-styrene with a shaping temperature inthe range of 170°-180° C. The external layers of polystyrene of this webmay be cooled down to the lower range of the shaping temperature.Besides good deep-draw ductility for the above described web, thearticles formed therefrom are of better mechanical quality than could bepreviously achieved.

It is a further main object of the invention to provide apparatus forthe manufacture of thin-walled thermoplastically shaped articlescomprising in sequence an extrusion device suited to receive granularthermoplastic material and to continuously compress and heat same untilliquefaction and a web-spraying mold as in the form of a fish-tailnozzle connected to the extrusion device and provided with temperatureregulators, a stabilizing and cooling device directly receiving the webfrom the nozzle and having cooling elements contacting directly bothsides of the web and conducting heat away and preferably connected toregulators adjusting the applied cooling temperature, a thermal formingdevice to shape articles from the web by deep-drawing or stamping anddevices for cutting the articles from the web. By means of thisequipment, molded articles may be line-produced, preferably fromgranular synthetics, this equipment being marked by reliable, rapidoperation because the hot plastic web will be immediately stabilized inthe cooling device to an extent sufficient for further processingwithout losing appreciable amounts of the heat stored in it, so that thestored heat of extrusion suffices entirely for the thermal formingprocess and no auxiliary or extra heating equipment may be needed.

It is further an object of the invention to provide for the foregoingapparatus above novel apparatus components for converting continuousadvance of the stabilized web into intermittent advance toward thethermal forming device.

Another object of the invention is to provide in the foregoing apparatusa dwell station where the recently formed and stabilized web will be setfor desired uniform surface temperatures prior to the thermal formingoperation. Specific to this object a tempering device at the dwellstation may be provided which will set the desired surface temperatureonly at definite web surface areas, for example the forming areas or theboundaries.

It is a further object of the invention to provide for the foregoingapparatus a radiation-temperature measuring instrument at the dwellstation and automatic control for the stabilizing and cooling device andfor the extrusion and thermal shaping device, this automatic controlbeing independent of the desired forming temperature when controllingthe temperature, and consisting in:

a. changing the length of the heat exchange contact between web surfacesand cooling elements of the stabilizing and cooling device, for instanceby altering the looping angle of the web around one or more coolingrollers;

b. changing temperature in the cooling medium in the stabilizing andcooling device; and

c. changing the frequency of operation of the thermal forming device.

If one wishes avoiding altering the weights of the manufactured articleson account of changes in the frequency of operation of the thermalshaping device, one must simultaneously undertake an alteration in theoutput of the extrusion device and the web-spraying mold. The foregoingcontrols should be automatically introduced in the sequence by means ofthe regulation device if each preceding measure no longer shouldsuffice.

Another object of the invention is to provide in apparatus of theforegoing type, a thermal forming arrangement comprising apparatus forpressing one web surface against a shaped die surface by applying afluid pressure to the other web surface.

A further object of the invention is to provide compact apparatus forthe manufacture of thin-walled, thermoplastically shaped articles,comprising:

devices for feeding and moving hot thermoplastic webs;

devices for surface tempering the webs to a temperature suitable forthermal forming;

a thermal forming device for making shaped articles from the web bydeep-drawing or stamping;

at least one vertically movable die support for the thermal shapingdevice;

and synchronously related drives for the thermal forming device and forthe devices for feeding and moving the webs, wherein related camscontrol vertical movement of the die support and the advance motions forthe webs; and the drives are equipped with adjusting devices to regulatethe vertical motions of the die supports to correspond to the size ofthe articles to be manufactured and to trim the web motions to therequired length and characteristics for each operational sequence as:

devices for stamping the shaped articles from the web;

devices for removing the formed articles, and

devices for removing the web residues.

Further objects of the invention comprise in the foregoing apparatusnovel detail such as shock absorbing and damping mechanism at thethermal forming station, and novel motor driven cam and belt drivearrangements for controlling operation of the various stations in theapparatus in desired synchronism, usually adjustable.

A further important object of the invention consists in creatingapparatus of the above indicated kind, wherein the web at the shapingtemperature will be precooled prior to thermal shaping outside the areaswhich are to be formed into the shaped articles in order to strengthenthe residual material areas surrounding the shaped articles andeliminate the necessity for unduly long cooling periods. This is ofspecial significance if the wall thickness of the shaped articles isappreciably less than the thickness of the web. For example, within thescope of the invention, it is feasible to thermally form in a web about2.5mm thick shaped articles which are only 0.5 to 0.6mm in wallthickness.

The cooling time required for the solidification of the material being aquadratic function of the material's thickness, solidification ofresidual material that has remained at its initial thickness andtemperature would require a cooling time about twenty times greater thanthe thinner shaped areas of the web. Even though it may not beabsolutely indispensable that the residual material surrounding theareas of the shaped articles be completely cooled and solidified, acertain degree of cooling and solidification may be required in order toreliably convey the web with the shaped articles to the next treatingstation, for a stamping station. By precooling those web parts which arenot to be formed, the time required for minimal cooling andsolidification of the non-shaped parts of the web will be better relatedto the times required for cooling the shaped articles. Precooling alsoallows appreciably better control of the shrinking effects occuring inthe residual material.

A further object of the invention lies in providing precooling devices,which are to be mounted, in direction of conveying of the web, upstreamof the thermal die means at the thermal forming station and which aremoved synchronously with the thermal die means.

It is a further object of the invention to provide at least onecooperating pair of precooling device and counter-precooling device,which pair(s) comprise(s) cooperating related positive and negativeshaping components in order to impart a framelike bracing structure intothe web during precooling.

A further object of the invention lies in providing a novel In-Lineprocess and a novel apparatus of the kind described above for thecontinuous manufacture of thin-walled shaped articles from thermoplasticmaterials, where

a. the stabilized web at the shaping temperature is passed through thethermal forming station in essentially vertical motion and where theshaped articles are formed out of the web in an essentially horizontaldirection; and

b. where the shaped articles simultaneously or within the same stage asthermal forming are separated from the web and may be further cooledeven after this separation.

Thereby is created a novel feasibility of forming and processingrelatively thick plastic webs, for example exceeding 3mm in thickness,by means of the above In-Line process. The shaping and working of suchthick webs in the In-Line process offers the feasibility ofmanufacturing articles with depth dimensions much in excess of thediameters of the apertures or of other opening dimensions. The verythick webs shaped in the In-Line process however are especially soft anddelicate and therefore prior to the invention could not be worked inordinary thermal forming processes and machines, especially if the webhad to be advanced horizontally. Nor was it possible prior to theinvention to adequately solidify the areas of residual materialsurrounding the shaped articles for such thick webs during the In-Lineprocess, so that the web with its shaped articles therein could bereliably conveyed to a further treating station. Nor was this possiblein the absence of precooling the web in those areas which were not to beshaped. The vertical conveying of the web through the thermal shapingstation and the cutting-out of the shaped articles all in one stage withthermal shaping, as well as post-cooling of the shaped articles, hasprovided new possibilities for the forming and working of very thickwebs in the In-Line process.

A further object of the invention lies in achieving vertical downwardconveying of the web, for a thermal forming apparatus of the kinddescribed earlier, in order to minimize transportation effects on theweb.

A further object of the invention lies in providing a thermal formingapparatus having a die support that may swing about a horizontal axis,such support holding two or more dies or multiple dies, rotationalpositions of the die support being provided for in each of which a dieor a multiple die will be opposite the web to be shaped. This rotatingdie support allows leaving the shaped article after thermal formingproper in the die for a certain time and acts to cool it even further bycontact with the die surfaces.

Finally, it is an object of the invention to provide devices forremoving the shaped articles from the web in apparatus of the abovedescribed kind with vertical conveying of the web, embodying separatorsassociated with the tools but thermally insulated from them and usuallyin the form of a recessed vertical plate, the dies being introduced inthese recesses at their aperture rims with horizontal play, and the rimsof these recesses providing separation edges coacting with the secondparts of the separation devices. In this manner one obtains separationdevices eliminating the difficulties that have been encountered prior tothe invention in attempting thermal shaping and simultaneous separationof the shaped articles from the web. Neither part of the separationdevice need be heated during thermal forming, so that thermal expansionphenomena no longer need being considered. The two cooperating parts ofthe separation device may therefore precisely fit together during theentire operation of the machine and effect a smooth clean cut.

Further objects, characteristics and advantages of the invention will befound in the description below of several embodiments illustrated in thedrawing. However, these embodiments should be considered illustrativeonly and in no sense restrictive of the scope of the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagrammatic view showing a method and apparatus for formingthin-walled articles from thermoplastic material wherein a thermoplasticweb is initially formed from one source of material, according to oneembodiment;

FIG. 2 is a diagrammatic view showing the method and apparatus in anembodiment incorporating two sources of thermoplastic material producinga composite laminated web;

FIG. 3 is a diagrammatic view showing the method and apparatus in anembodiment incorporating three sources of thermoplastic materialproducing a composite laminated web;

FIGS. 4A and 4B are graphic views illustrating temperature relationshipsin a thermoplastic in the invention;

FIG. 4C is an enlarged fragmentary view partly in section illustratinginternal web conditions;

FIGS. 5A and 5B are enlarged fragmentary views in section illustratingweb shaping operations;

FIG. 6 is a fragmentary side view showing an arrangement for webstabilization;

FIG. 7 is a fragmentary side view showing another arrangement for webstabilization;

FIG. 8 is a fragmentary view showing means controlling a compensatingroller of a stabilization arrangement;

FIG. 9 is a fragmentary side elevation showing a dwell station in theforming apparatus;

FIGS. 10, 11 and 12 are fragmentary side elevations showing threedifferent forms of dwell stations;

FIGS. 13 and 14 are sectional views illutrating two different aspects ofthermal forming;

FIG. 15 is a diagrammatic side elevation showing a drive system for athermal forming device in association with a thermoplastic web castingmachine for producing the web to be shaped;

FIG. 16 is a side elevation partly in section showing the drive systemfor thermal forming means with some modification;

FIG. 17 is a side elevation partly in section showing a thermal formingmeans that is a variation of that of FIG. 16;

FIG. 18 is a side elevation partly in section showing a thermal formingmeans to be used in connection with the present invention and containinga two step precooling means;

FIG. 19 is a top view of a thermoplastic web treated by thermal formingmeans according to FIG. 18;

FIG. 20 is a partly cut away side elevation partly in section showing athermal forming means that is a variation of that of FIG. 18;

FIG. 21 is a side elevation partly in section and partly cut awayshowing a detail of the apparatus of FIG. 20 in closed position;

FIG. 22 is a top view of a thermoplastic web treated by the thermalforming means of FIGS. 20 and 21;

FIG. 23 is a sectional view along line 23--23 of FIG. 22;

FIG. 24 is a side elevation showing a further embodiment of an apparatusfor forming thin-walled articles from thermoplastic material wherein arelatively thick web is initially formed from a source of material; and

FIG. 25 is a sectional view substantially along the line 25--25 of FIG.24.

PREFERRED EMBODIMENTS

FIG. 1 illustrates the operational sequence and the basic design of theapparatus as constructed and arranged for the manufacture ofthin-walled, thermoplastically shaped articles. It comprises at leastone extrusion device 1 suitable for receiving granular thermoplasticmaterial and compressing and heating it continuously until liquified.The liquified thermoplastic material processed by extrusion device 1 isconveyed into a web spraying mold 2, preferably fashioned as a fish-tailnozzle and provided with temperature regulators.

The hot plastic web I continuously issuing from nozzle 2 is immediatelyfed to a stabilizing station 3 where the web is stabilized by precoolingits opposite surfaces in such fashion that thin partly solidified butstill deformable supportive layers or shells of said thermoplasticmaterial will be produced at those surfaces whereby the web alreadybecomes self supporting, but the inner material of the web remainsessentially at about the extrusion temperature and in a very plasticstate.

The continuously advancing web from stabilizing station 3 is fed to amotion control feed conversion device 4 for converting the continuousadvance of the web into intermittent advance.

The intermittently advanced web passes through a dwell station 5 wherethe recently formed and surface cooled stabilized web is subjected to atemperature compensation treatment and set for the proper surfacetemperature required for thermal shaping.

The web is then advanced to and subjected to thermal shaping at thethermal shaping station 6 where a mechanically acting stretching elementmay be applied to one web surface to urge the other precooled websurface against a shaping tool surface where it is further cooled.Alternatively the web at least temporarily may be subjected at theshaping station to compressed air at one of the precooled surfaces andthereby have its other surface pressed against the shaping tool surfacewhere it is further cooled.

The web is now fed into stamping station 7. Following stamping-out ofthe shaped articles at station 7, the residual web is brought to areceiving station 8 provided with a suitable device 81 for reducing theweb material into granular form, so that this residual material may befed back and recycled through a metering device 82 to mix with the freshmaterial at extrusion device 1 in a predetermined ratio.

A further embodiment is shown in FIG. 2. In this example, a first kindof thermoplastic material is compressed and heated until liquefaction ina first extrusion device 11 and extruded and conveyed under pressure toa slit-like nozzle 2. Thermoplastic material of a second kind iscompressed and heated in a second extrusion device 12 until liquefactionand deposited in a layer as a sheath or strip on the surface of the webof first material upstream of nozzle 2. The superposed layers enteringnozzle 2 are cast into a continuous composite laminated plastic web IIissuing from nozzle 2.

Composite thermoplastic web II is now processed in succession throughthe stabilizing station 3, the feed conversion device 4, dwell station5, thermal forming station 6 and stamping station 7 as in FIG. 1. Thecomposite web so produced if formed at the stabilization station withopposite surface layers that are partly solidified but still deformable,and interiorly the different overlying thermoplastic materials are stillsubstantially at extrusion temperature and their contacting surfacesremain quite fluid. The extrusion device of FIG. 2 may consist of morethan two extruders discharging together into a composite web sprayingnozzle 2.

A composite web II so manufactured may evidence properties at one orboth precooled outer surfaces which are different from those at the hotplastic core. For example, where two different kinds of material arelaminated, the first material may be a standard polystyrene, and theother material may be an impact resistant plastic such as abutadiene-rubber modified polystyrene. The composite web may alsoinclude outer layers of the impact resistant plastic on both surfaces ofa standard polystyrene web, the precooled surface layers being formed onthe outer webs while the materials internally of those layers all remainsubstantially at extrusion temperatures.

However, one may also make a composite web II with polyolefins, with forexample polypropylene or polyethylene at the outer surface or surfaces,and with polystyrene or with polystyrene reacted with butadiene-rubberat the core. Adhesion of these differing thermoplastics may be achievedand/or improved by means of additionally and simultaneously extrudedadhesives in a known manner. As is known per se, both polyethylene andpolypropylene have the following properties:

a. their forming temperature range in the crystalline melting pointrange is narrow;

b. they must be shaped at high forming temperatures;

c. both, but especially polypropylene, may not be heated without airsupport in conventional thermal shaping because the foils will stronglysag shortly above the crystalline melting point which will cause marked,interfering folds in the die;

d. they require very even temperature distribution over the shapingsurface (due to danger of crystalline residues and making folds).

The invention takes the foregoing into consideration and enablesmaintaining the temperatures very evenly and sufficiently high for verysmall and controlled cooling, especially at the temperature compensationdwell station. There is no need to fear premature cooling of the webbecause the inner layer, whether of standard polystyrene or theimpact-resistant polystyrene, will steadily and uniformly release heatto the outer polyolefin or other layer or layers. There is no tendencytoward sagging of the composite web because the hot internal layer ofthe first material will not tend to sag even if the layer is subjectedto the temperature required for shaping the outer polyolefin layer orlayers (ca. 170° C = 340° F). Parts shaped from a composite web II witha polypropylene outer layer or layers are particularly shape retainingat higher temperatures.

One may further achieve a composite web II where the outer surfacethermoplastic material is a polycarbonate and the core material astandard polystyrene or an impact-resistant, butadiene-rubber modifiedpolystyrene. Shaped articles may be made in this manner which willmaintain their shapes up to temperature ranges of 130° to 135° C(266-275° F), and will be weather-resistant, of high gloss andnevertheless economical.

As the polycarbonate foils are per se highly hygroscopic, the longersuch foils are kept sandwiched, the larger the danger of bubbleformation during thermal forming and the danger of reduced mechanicalstrength. The bubble formation, which is also determined by thermaldecay, increases with foil temperature. However, the invention allowsthe processing of composite polycarbonate foils of the foregoing typewithout being subjected to these drawbacks, because:

a. there is no sandwiching of the web; and

b. polycarbonates may be thermally shaped at relatively lowtemperatures, mainly because the internal or carrier layer may bethermally shaped because of the retained heat of extrusion.

The process of the invention when applied to composite webs with outershells or layers of polycarbonate may be so carried out that thecomposite web surfaces are maintained nearly cold while the core howeverremains hot. This is an appreciable difference as compared to theprocesses discussed within the scope of the invention for forming web IIhaving polyolefin outer layers, where the outer layers may be cooledessentially only slightly for stabilization and where core reheating mayoccur for thermal forming.

The scope of the invention also allows making the outer layer of layersof composite web II of standard polystyrene or of an impact-proofbutadiene-rubber modified polystyrene of a shaping temperature in therange 130°-140° C (266°-284° F), while the core material may bepoly-alpha-methylstyrene with a shaping temperature in the range170°-180° C (338°-356° F). Besides good thermal shaping properties,articles made from such composite webs evidence mechanical qualitiespreviously unattainable.

FIG. 3 shows a further modification of the apparatus for manufacturingthe plastic web, with devices for uniting several extruded webcomponents of different or the same materials into a composite web III.Extrusion device 1 here consists of three extruders casting their webcomponents through wide slit nozzles 21-23 to form three thermoplasticwebs that are superposed and moved over a pressure roll pass 24, 25which, when applying slight pressures to each of the individual webs,unites them into a single multilayer composite web III. Furtherprocessing of this composite web proceeds in the same manner as for thewebs in FIGS. 1 and 2.

Referring to FIG. 3, one may compress and heat a thermoplastic materialof a first kind to liquefaction in extruder 11 and then cast it as aplastic web component from slit-like nozzle 21. A thermoplastic materialof a second kind may be compressed and heated to liquefaction inextruder 12 and cast as a second plastic web component from slit-likenozzle 22. Either the thermoplastic material of this second kind or oneof a third kind may be compressed and heated to liquefaction in extruder13 and cast as a third plastic web component from slit-like nozzle 23.In this manner may be combined even the most diverse materials which mayalso differ markedly with respect to temperature behavior.

It is important that extrusion of the continuous hot thermoplastic websI, II is executed at the upper temperature limit of the temperatureregion in which the respective material is in a plastified condition.This region is indicated at γ in FIGS. 4A and 4B. This means that whenexceeding such upper temperature limit plastified material as it leavesthe nozzles cannot be in the form of a web capable of being shaped. Thisalso means that the extrusion temperature is such that the web leavingthe nozzle 2 of FIGS. 1 and 2 or leaving nozzle 313 of FIG. 24 orleaving nozzles 21, 22, 23 of FIG. 3 in any case is strong enough andsufficiently self-supporting to be transported to the chilling andstabilizing station 3.

The absolute values of extrusion temperature increase are different frommaterial to material and there may be many different types of the samekind of material which must be extruded at different temperatures.

In an example, standard polystyrene (general purpose polystyrene 165 Hof BASF) may be extruded at an extrusion temperature in the range of200° to 220° C, the temperature being usually dependent of the type andbatch of material and thickness of the web, but when running in aproduction line for making thin walled articles according to the presentinvention one may begin at 200° C and carefully increase the extrusiontemperature so long as stable processing is maintained. The temperaturesat the cooled web when entering the thermoforming step may be 115 to140° while the core material is 140° to 170° C, a minimum difference ofabout 25° C being maintained in the range.

In a further example, in a mixture of 50% general purpose polystyrene(BASF 165 H) and 50% high impact polystyrol BASF 476 L), the relativeextrusion temperature and core and outer surface layer temperatures areabout the same as in the first example.

An important feature of the invention is that the plastic web afterhaving left the extrusion nozzle is not only precooled but it is rapidlyand uniformly chilled at both its surfaces. Such chilling means that inthe relatively thin outer surface regions along the web the temperatureof the material is rapidly and suddenly decreased below the lower limitof the formability temperature range. When the thermoplastic material isso cooled it exhibits more or less steady transition regions between theouter thin solidified elastic layers and the still hot fluent liquidcore. The various temperature identifiable conditions present in the webin the invention are illustrated in FIGS. 4A and 4B where:

α is the solidified condition range;

β is the elastic plastified condition range in which the material isthermoformable and some molecular orientation is caused when shaping thematerial especially when deep drawing;

γ is the plastified fluid condition range in which the material isextrudable so that no molecular orientation is caused during extrusion,and

δ is the liquid condition range.

FIG. 4A is a diagram graphically illustrating temperature gradientconditions across different plasticized webs.

Curve A shows the temperature gradient in a plasticized web heated bythe previously conventional method of surface irradiation. It will benoted that the outer surface temperature is appreciably higher than atthe center of the web. Because conventional processes for shapingrequire a minimum forming temperature to be present at the web center,the temperature at the web surfaces must necessarily be appreciablyhigher in view of the poor thermal conductivity of thermoplasticmaterials.

Curve B₁ of FIG. 4A shows the temperature gradient in a plasticized webwhich had been extruded in a conventional method and is thermoformeddirectly. In such extruding and direct thermoforming the extrusiontemperature is controlled to be as low as possible in order that theextruded web can be manipulated to be transported to the thermoformingmeans. In such methods (known by German Auslegeschrift 1,165,241 andShelby U.S. Pat. No. 2,891,980) the web temperatures are as low aspossible during extrusion so that the web may be immediately fed to theformer.

Curve B₂ of FIG. 4A shows the temperature gradient in a plasticized webmade by extrusion similar to that discussed above in connection withcurve B₁, but after the web has been precooled as it has already beenproposed by Crenshaw U.S. Pat. No. 3,354,693. Such precooling causes thetemperature at the inner regions of the web to decrease substantiallydue to heat transport during the precooling time. After the materialattains a temperature gradient as shown by curve B₂ shaping is onlypossible if the web is not deeply formed, but for deep-drawing or otherdeep thermoforming the material must be cooled so much that the articlewall would be stretched at an intolerable rate.

Curve C of FIG. 4A shows the temperature gradient in a plasticized webwhich in accord with the present invention has been prepared forthermoforming. Such a web has been stabilized by chilling over itsentire opposite surfaces directly after it has been extruded from thenozzle. Such chilling results in two outer stiffened supporting surfacelayers or shells and a very warm web core. As chilling involves a veryrapid temperature decrease at the web surfaces there is no time for heattransport from the inner core region to the outer surface regions of theweb during the chilling step. For this reason the surface layers orshells are relatively thin.

When thermoforming a web having a temperature gradient as shown in curveC, the thermoplastic material of the outer surface layers is in asomewhat elastic plasticized state or condition. When deep-drawing orotherwise thermoforming in such relatively low temperature materialthere is caused a characteristic molecular orientation with respect tothe drawing direction. Such molecular orientation will also occur in thesomewhat inner regions which will be cooled during the deep-drawing orother thermoforming whereas the innermost hot core material will remainin relatively fluid plasticized condition and will be redistributedduring the last step of thermoforming, when the preshaped outer shellportions are pressed toward each other and relatively shifted withrespect to each other. Thus the fluid inner core material provides avery uniform material distribution and the shaping steps are finishedbefore such hot inner core material has cooled sufficiently to developmolecular orientation. Additionally the lower temperatures indicated bycurve C for the supportive web surfaces and the maintenance ofrelatively high temperatures at the core also decreases the sensitivityof the web with respect to area tempering through cooling with colddies. The lower web surface temperature ensures that, upon touching thecold die surfaces, no undue amount of heat will be transferred from theweb to the dies, particularly locally. Also the hot fluid core acts as aheat reservoir to effectively reheat the outer surfaces as the web movesfrom the chilling station, and such removes the danger of there beingchill marks on the product article surfaces.

The surface temperatures during forming are relatively low and thetemperature differences with respect to the cool die surfaces at theshaping station are advantageously low. This eliminates to a greatextent the danger of setting up stresses in the final product. The twoouter supportive surfaces undergo stretching in the shaping process andare connected to each other by the relatively fluid elastic core thatremains heated extremely close to the melting point or extrusiontemperature, so that each of these surfaces may be differently shaped soas to correspond with a desired end product. A very uniform materialdistribution is thus obtained, with no voids or weakened regions, theattainment of which has always presented a serious problem in previousprocesses using thermal forming.

FIG. 4B shows curve C in comparison with some temperature gradientcurves which could be realized during the several steps of the methodaccording to the present invention. Curve C₂ shows the temperaturegradient in the plastic web when leaving the extrusion nozzle. In theinvention this extrusion temperature is much higher, for example 50° Chigher, than the normal extrusion temperature for such material such asis used in the Crenshaw patent process for example. As may be seen fromFIG. 4B the extrusion temperature is very close to the upper limit ofthe extrusion temperature γ in which the extruded material is in a fluidcondition, whereas in the upper temperature stage δ beyond the abovementioned limit the material would be so fluid and liquid that it merelywould drop down when leaving the extrusion nozzle and would not be ableto hold together and support itself as a web. Immediately after leavingthe extrusion nozzle the web is stabilized by being chilled at both itssurfaces by contact with cool heat transferring surfaces. By suchchilling a desirable temperature gradient across the web may be realizedas shown in curve C₁.

As thus may be seen from curve C₁ on each of the web surfaces a thinouter surface layer is produced which is so cool that the material is ina solidified condition at a temperature below the somewhat elasticplasticized condition of the thermoforming temperature range β. Thismeans that after chilling the outer surface layers of the web at firstmay be so hard that they would not be thermoformable, whereas the mainpart of the material is maintained practically fluid at its extrusiontemperature extremely close to the upper limit of extrusion temperaturerange. In such condition the web may be easily transported andmanipulated, but experience has shown that it would not be advisable tothermoform the web in the condition of curve C₁.

During transportation of the web from the chilling station 3 to thethermoforming station 6, heat balancing distribution will occur in theweb. This means that some heat is transferred by conduction from the hotcore c to the cooled surface layers l. This heat transfer results in theweb attaining the condition of curve C in FIG. 4B, wherein the outersurface layers have been reheated to a temperature in the range β andare in elastic plastic condition. The outer surface layers l built up bythe material in the somewhat elastic plasticized condition and withinthe temperature range β may become progressively thicker as illustratedin FIG. 4C and such built up material will become reheated by heatderived from the core to a temperature preferably substantially at thelower limit of the temperature range β. Due to such reheating thesurface layers may be readily thermoformed with development of molecularorientation as pointed out above. The foregoing reheating step takesplace mainly at the dwell station 5 in FIGS. 1-3.

FIGS. 5A and 5B diagrammatically show the behavior of a composite web ofthe invention during the thermal shaping or drawing operation at station6. Points or regions X and X' at opposite surfaces of the web, which asshown in FIG. 5A were directly opposite one another prior to the thermalforming process, have been relatively shifted during forming inaccordance with the geometry of the desired article as shown in FIG. 5B.Effectively the opposite shells of the web, whether a single componentor composite web, may thus be differently shaped without undesirablystressing the web. The core's temperature is very near the melting orextrusion point and during thermal shaping the relatively elastic fluidcore will be distributed evenly and freely by stresses acting betweenthe two relatively moving outer layers or shells at the outer surfaces.At the relatively cool outer surface layers 1' of the web during drawingor other thermoforming, molecular orientation is caused, substantiallyin the drawing direction. As forming proceeds the web progressivelycools and the outer surface layers are further built up in thickness asshown at 1² in FIGS. 4C and 5B. As the surface layers increase inthickness the outermost regions will have a very strong molecularorientation and the inner regions of such surface layers will have lessmolecular orientation. Summarizing, this means that a wall condition ofthe article can be obtained in which the outer surface regions have astrong molecular reorientation and there is a continuous gradualtransition to little or no reorientation to the inner wall region.

Articles shaped in accordance with the invention will therefore break orrupture much less rapidly than those manufactured conventionally,especially since the latter suffer from oxidation disintegration due tothe high surface temperatures and from the ensuing brittleness usuallyaffecting deep drawn articles.

FIG. 6 shows apparatus for the stabilization of the continuously movinghot plastic composite web I at station 3. The web is stabilizedimmediately upon leaving nozzle 2 and it is made to pass through asurface cooling arrangement, here in the form of rollers that coolopposite web surfaces similarly and the relative positions of which maybe adjusted to vary the heat conducting and heat exchange areas ofcontact, by changing the web areas in contact with rollers 31 and 33without changing the length of the continuously moving web betweenroller 33 and roller 42 of the next station 4. The angular extent of weblooping around the cooling rolls may be set as needed to achieve thisresult in the apparatus of FIG. 6. A rotatable cooling roller 31 isslidably movable along a guide 32 essentially in the shape of a circulararc of about 90° extent around the center of an opposite fixed axisrotatable cooling roller 33. A displaced position of roller 31 is shownin dot-dash lines at 31' and the corresponding changed path of the webindicated at I'. This illustrates the infinite adjustability of thecooling arrangement.

The stabilization apparatus is followed by apparatus for converting thecontinuous web advance into intermittent or step-wise advance as bycompensating roller 41 and deflection rollers 42 and 43 as will bedescribed later.

FIG. 7 shows a modification of the apparatus for stabilizing a hotplasticized composite web. Web I in this example is guided horizontallyas by a V-shaped arrangement of rotatable cooling or tempering rollers34, 35 and 36. These latter include essentially a tempering roller 35axially fixed in position above web I and two rollers 34 and 36 locatedrespectively between fixed axis guide rollers 37' and 38' and the fixedaxis tempering roller 35. Rollers 34 and 36 are suitably mounted forvertical adjustment between the lower dot-dash line position shown inFIG. 7 at 34' and 36' respectively and the upper solid line position, asindicated by the double arrows 37 and 38. Thus, different areas ofcontact between the cooling rollers and continuously moving web may beobtained whereby the opposite surfaces of the web may be simultaneouslyand similarly precooled or surfaced tempered at to effect differentshell compositions or outer supportive layer thicknesses along theopposite surfaces. Besides altering the length of the heat exchangecontact of the web surfaces with all of the cooling rollers, the sameeffect may be attained by changing the looping angle of the web aroundany cooling roller. It is also possible to control the stabilizationprocess by varying the temperature of the cooling medium in one or moreof the cooling rollers without adjusting the areas of web contact, or inassociation with such adjustment. This could be done for example byconnecting roller 33 or 31 or both to internally received cooling liquidfrom a source having a control for varying the temperature of thecooling liquid.

FIG. 8 shows a control apparatus at station 4 for the purpose ofconverting continuous web advance into step-wise advance. Thecompensating roller 41 shown here preferably is controlled by means ofthe illustrated belt or chain drive, sprocket wheels being mounted atthe front side of compensating roller 41 and at the front sides of fixedaxis guide rollers 42 and 43. The sprocket at 42 is continuously driven.The sprocket at 43 is intermittently driven at a frequency correspondingto the dwell time needed for the operations at the succeedingtemperature compensation, thermal shaping and cutout stations.Compensating roller 41 is suitably guided for free movement verticallyas indicated by the double arrow 44. The compensating roller 41 may beso controlled as by suitable biasing springs (not shown) that the webwill be fed substantially free of tension. It must be arranged in thisrespect that output of the thermal forming device 6 and that of theextrusion device will be so correlated that the compensating roller 41never reaches one or the other possible vertical terminal positions evenduring long time operation. It may happen that rapid and intermittentmotion past the dwell station 5 into the thermal shaper at 6 will causehigh accelerations. The weight of the web must be added to theseeffects, and the limit may be set by the inherent weight of the web, sothat it may not be subjected to stretching when rapid step-wise motionoccurs. To prevent this from happening, compensating roller 41 isemployed, and expecially when dealing with thin webs, it will preferablyoperate from top to bottom, because the momentary acceleration duringmotion is near in value to the acceleration of free fall (g = 9.81m/sec2), so that the weight of the web and the forces of accelerationwill compensate, and for exact compensation, the web will be more orless in free if controlled fall. The compensating roller 41 and theguide rollers 42 and 43 in every case preferably are as nearly aspossible thermally neutral, that is, they may neither heat nor cool theweb. This is preferably achieved by using a very thin sheet metal rollerat 41 with an insulator covering such as felt or another textile thatwill very rapidly reach a certain temperature and thereafter neitherwithdraw nor impart heat from and to the web.

Since roller 41 is spring biased upwardly in FIG. 8, as the web iscontinuously fed toward it the roller 41 will rise vertically toincrease the loop between rollers 42 and 43. Then as the intermittentfeed at 43 is actuated the web will be pulled out of the loop fasterthan it enters it, such being controllably permitted by roller 41displacing downwardly to shorten the loop for the period of theintermittent feed stroke. This cycle is repeated at each intermittentweb feed stroke. It will be understood that the invention in its broaderphases contemplates any suitable intermittent web feed apparatus atstation 4.

FIGS. 9-12 are illustrative of an important phase of the inventionrelating to the dwell station 5 where the opposite web surfaces aretreated for providing uniform temperature thereacross.

In thermal forming it is extremely important and desirable that there beas completely uniform temperature across the web surfaces as possible.At station 5 the web is treated for that purpose.

As shown in FIG. 9 the web, which at this point is relatively warm sinceit consists essentially of a hot plastic inner core having thinsupportive layers or shells on and along opposite surfaces, passeshorizontally between similar upper and lower parallel reflector members5' having their reflecting surfaces facing the adjacent web surfaces.The reflectors may be polished aluminum which are good heat reflectors.As shown in FIG. 9 each reflector member 5' is provided with a series ofincreasingly spaced non-reflective areas or spaces 5b that providesuccessive reflecting areas 5a of increased size from left to rightwhereby radiant heat from the web will be proportionately reflected backto the web surfaces in varying degree by the different size reflectingareas 5a.

In operation with a section of web disposed between reflector members 5'as illustrated in FIG. 9 it will be appreciated that the amount of heatper unit area radiated from the web at region 51 is greater than thatradiated per unit area at region 52, for the reason that region 52 ismore distant from the extrusion device and hence has had time to cooldown more than region 51. By providing smaller heat reflective areas 5aopposite the warmer web portions and gradually compensatively increasingthose areas in size toward the cooler web portions, the web surfacesbetween the reflector members are raised to uniform temperatures overtheir entire areas. The same effect may be produced by making reflectionareas 5a of increasingly greater heat reflective value, instead ofincreased size, from left to right in FIG. 9.

A further possibility for the dwell station 5 is shown in FIG. 10. Inthis instance zig-zag reflectors 5c of various angles are used, thechanging relative angular positions of the reflectors progressivelydetermining the desired reflectivity, such that more heat will bereflected back to the web at the right side of the station opposite webregion 52 because of the more oblique position of the reflectors withrespect to the colder web region 52.

Another advantageous embodiment of dwell station 5 is shown in FIG. 11.The lower web surface, which will face the tool in the thermal formingstation 6 later to be described, contacts a tempering device 53 for heatexchange by conduction, and only certain areas of the web, for instanceonly the areas to be shaped or the edges will be maintained a fixedtemperature, which may deviate from that of the remaining areas. In thismanner it is possible to achieve extremely favorable shaping of the web.The web contacting areas of device 53 are maintained at the desiredtemperature by passing a heated fluid through the illustrated passages.

A further embodiment of dwell station 5 is shown in FIG. 12. Dependingon the characteristics and properties of the thermoplastic web, certainmaterials may require an air circulation chamber keeping the plastic webat a constant temperature. This applies particularly to polymers forwhich thermal shaping must take place in an extremely criticaltemperature processing range. It is known for example that modifiedpolystyrene allows a temperature range of ±10° C (18° F) within whichthe product will not be affected. This temperature range is still morenarrow for polyolefins and polycarbonates, so that the above disclosedreflector arrangements may not suffice. The station 5 circulationchamber is not meant to increase temperature overall but rather tomaintain a desired temperature by compensatively distributing the warmair over the web surfaces between regions 51 and 52. The web surfacetemperature distribution will be the most uniform if the circulating airis made to move in a direction opposite to the advance of the web asshown by the arrows in FIG. 12. There may be one fan 54 and one heater55 for each of the upper and lower parts of chamber 5d to setcirculation at the required degree.

Various possibilities are diagrammatically shown in FIGS. 13 and 14 forthermal shaping at station 6. A negative die is shown in FIG. 13,working together with a stretching element 61 which is coated at the webengaging surface with a heat-insulating, porous layer, for example afelt layer 63. Element 61 is provided with an inlet bore 60 andbranching bore holes 64 adapted to be connected to supply compressed airwhich will be finely distributed by the felt covering 63. The interiorof the negative die 62 is provided at the other side of the web withevacuation bores 65 allowing timed application of vacuum. The design andthe operation of such shaping devices are known per se. However, asshown in FIG. 13, in the invention the outer layers Ia of the web arelike shells holding between them the hot fluid plastic core Ib. Whencompressed air is supplied through bore 60 and vacuum is connected tobores 65 the felt layer 63 and the cooled metal inner cavity surface ofthe die negative 62 contact the opposed shell like surfaces of the webto form the article shape. This action causes distribution of theexternal mechanical forces in the plastic core Ib, which in turnenhances internal distribution of the plastic between the shells whenthe web is pressed against the inner surface of die 62 under thecombined influence of the vacuum from bore 65 and pressure from bore 64.

The example of FIG. 14 shows a positive forming device with coactingpositive and negative rigid die elements 66 and 67. The positivestamping tool or male die 66 and the negative stamping tool or femaledie 67 are in intimate contact with the opposite shell-like outersurfaces Ia of the plastic web, so that these outer surfaces will takeon the form of the dies 66 and 67. During pressing of the latter towardeach other, the plastic core of the web will be distributed between theshells and in practice the fluid plastic material of hot core Ib actshydraulically on the shell like outer surfaces and therefore ensuresvery good and solid contact with the surface contours of dies 66 and 67.

The forming devices shown in FIGS. 13 and 14 are only examples. Anyknown thermal shaping process or any known thermal shaping equipment maybe applied within the scope of the invention. The process of theinvention in substantially every case will provide advantages because ofthe pre-formed shells or outer supportive surfaces of the web to beformed.

Referring first to FIGS. 15-17, the main drive for the thermal formingapparatus comprises a cam and gear unit 101 powered by an electric motor(not shown). An output lever 102 controlled by cams inside the unit aswill appear actuates the forming dies, and output sprockets 103 and 104respectively provide sources of intermittent and continuous webmovements as will be described in detail. Vertically movable on one ormore stationary columns 107 rigid with the machine frame 108 are a lowerdie support 105 and an upper die support 106, and the composite web Ipasses between them to be intermittently stopped for the article formingoperation of station 6 of FIG. 1. The dies or tools shown in FIGS. 13,14, 20 or 21 respectively may be mounted on the supports 105 and 106, orother suitable shaping devices may be provided there.

Lever 102 is pivoted on fixed axis at 120, and is pivotally connected at113 to one end of a link rod 110. The other end of rod 110 is pivotallyconnected at 114 to one end of a lifter lever 109 pivoted intermediateits ends on a fixed axis shaft 121. The other end of lever 109 ispivotally connected at 122 to the lower end of a lift rod 111, and theupper end of rod 111 is pivotally connected at 123 to the lower diesupport 105. Lift rod 112 is operated from shaft 121 and pivotallyconnected to die support 106 at 125, in the manner shown in FIG. 18.

FIG. 15 shows the drive means used in connection with the presentinvention for a thermal shaping machine 157 following a plastic webextruder 156. A thermal shaping machine of this type is disclosed inThiel Pat. No. 3,836,309 issued Sept. 17, 1974. A cooling andstabilizing device 158 is connected to the plastic extruder, comprisingan idle counterpressure roller 161 functioning together with the firstcooling roller 159 to pass the extruded web. The second cooling roller160, as shown by double arrow 162, may be adjusted with respect toroller 159, in order to vary the looping angle of the web around bothcooling rollers 159 and 160 as in FIG. 6. Roller 159 is continuouslydriven from the continuously rotation sprocket wheel 104 of the cam andgear unit 101, as by the chain drive connection 163, 164.

A motion converter 165 similar to that of FIG. 8 is connected to followthe cooling and stabilizing device 158 and comprises an upward movingcompensating roller 166. Compensating roller 166 is held in a continuouschain arrangement 167 on its input side facing the spray-casting device156, that chain being driven from the continuously running chain linkage163. On the output side facing the thermal shaping machine 157,compensating roller 166 moves in an intermittently operating chainarrangement 168 which is driven in turn through drive 169 connected tointermittently operating chain 151 of advance device 152. Because of thecontinuous drive of the chain arrangement 167, the compensating rollerwill be steadily lifted in accordance with the supply of thecontinuously moving web, as long as the intermittently operable advancedevice 152 is stationary. When the thermal shaping machine 157operational sequence actuates the web advance device 152, the secondchain arrangement 168 of the compensating roller will also start runningand this causes the compensating roller to be lowered in proportion tothe web section to be supplied to the thermal shaping machine 157. Thetotal web advance is the same for both kinds of motion. This is ensuredby design of the drive devices of the cam and gear unit connected tosprocket wheels 103 and 104.

FIG. 15 shows an upwardly biased (springs not shown) compensating roller166. Motion converter 165 takes up the continuously supplied webarriving at constant average speed as compensation roller 166 movesupward, also overcoming the web inherent weight. During intermittentwithdrawal of the web, the more or less jerky motion occurs downward,that is, in the direction of the inherent weight of the web due togravity.

As shown by FIG. 15, the intermittently operating conveying device 152for the web may be of such length upstream of the thermal shapingmachine 157 that if necessary a temperature compensation dwell station 5may be placed between motion converter 165 and thermal shaping machine157. This compensation and stopping station may be of such length as tocorrespond to a single section or to several sections of an advance stepof the web effected by belt 152.

Referring to FIG. 16, output lever 102 carries at opposite corners apair of cam follower rollers 118 and 119 that respectively engage cams115 and 116 mounted on a shaft S continuously driven by the electricmotor. Rotation of shaft S causes selective cyclic rocking of lift lever109 during the forming operation, the nature of the rocking movementbeing controlled by cams 116 and 117.

The location of cam follower rollers 118 and 119 and the contours of camdisks 116 and 117 are so determined with respect to one another that thecam follower rollers will always be in contact with the peripheralsurfaces of the respective cam disks during operation. When roller 118enters a radially recessed part 116a of its cam 116, roller 119 will bein contact with a radially projecting part 117a of its cam 117. Roller119 proceeds inversely on a radially recessed part 117b of its cam 117when roller 118 runs on a radially projecting part 116b of its cam 116.In operation the movements of lever 102 under cam control aretransmitted through eccentric pin 113 to link rod 110 which in turn actsthrough eccentric pivot 114 to rock lifter 109 and actuate the diesupports. Cam 115 is continuously rotated by the electrical motor, whilethe vertical motion of die supports 105 and 106 is solely determined bythe peripheral shape of cam disks 116 and 117. Operational synchronismof die supports 105 and 106 may be varied by a continuously adjustablespeed reducer inserted between the motor and cam 115, or by changing themotor speed.

The eccentric pivot connections at 113 and 114 are adjustable as byrotatable and clampable eccentric pivot means. As shown in FIG. 16adjustment of eccentric pivot 113 may vary the length of effective leverarm X between pivots 113 and 120 of lever 102, while adjustment ofeccentric pivot 114 may vary the length of effective lever arm Y betweenpivots 114 and 121 of lift lever 109.

If lever arm X is set at its minimum length and lever arm Y is set atminimum length, such will result in maximum lift of die supports 105 and106. If lever arm X is set at minimum length and lever arm Y is set atmaximum length, such will result in minimum lift of the die supports.

The lift range may be continuously adjusted between minimum and maximum.By selecting the eccentric magnitudes with respect to the minimum valuesfor the lever arms X and Y, the range of the lift adjustment may bedetermined. In a current machine, a lift adjustment in the ratio of1:11/2 minimum: maximum is used.

To achieve self-locking performance of the dies, shaft 121, pivots 122and 123 of lift rod 111, and pivots 124 and 125 indicated in FIG. 17should be in a single, preferably vertical, plane in the closed positionof the dies as shown in FIG. 16. To achieve this, link rod 110 isadjustable in length, so that for any adjusted position of eccentricpivots 113 and 114, the desired self-locking position of the parts maybe set when the die is closed. So as to have the capability of settingdie support 105 for closed die position, lift rod 111 is also adjustablein length. Lift rods 112 also may be made adjustable in length asrequired.

FIG. 17 shows an embodiment of a thermal shaping machine, which issimilar to that of FIG. 16. The same reference numberals are used as inFIG. 16 for similar parts. The following modifications exist withrespect to FIG. 16:

1. In FIG. 17, the lift adjustment is not made by eccentric pivots as inFIG. 16, but instead by adjustment of a block 113a mounted for slidabledisplacement along a guide slot 113c in lever 102.

Adjustment of block 113a which is pivotally connected to link rod 110 isachieved by a threaded spindle 113b. The disclosed arrangement ofsliding block 113a on lever 102 provides the advantage of a longeradjustment path and also of a more rapid and continuous setting of thelift path. At the dwell state shown in FIG. 17, slot 113c extends alonga circular arc about the axis of the stud bearing at 114a which issimilar to stud 146, so that the rest state of lifter 109 will remainunaffected by adjustment of block 113a. In order to still furtherenlarge the range of lift adjustment, the stud bearing 114a shown inFIG. 17 may also be provided with a sliding adjustment (indicated butnot shown), by means of which the spacing Y between stud bearing 114aand axis of shaft 121 may be varied.

2. FIG. 17 shows the upper die support 106a with several, for example,three boreholes 125a vertically aligned one above the other. The pivot125 of lift rod 112 may be placed in any of those holes 125a to locateupper tool 190 at various heights. (FIG. 17 shows a tentering frame asan example of an upper tool 190).

3. The embodiment of a thermal shaping machine shown in FIG. 17 isprovided with two pressure cylinders 180, preferably pneumatic, that aredouble-acting and located at the lower die support 105, and theyeliminate conventional ejector springs. Such ejector springs on accountof their bulk requirements in the tools, the difficulty in determinationtheir moments of force, their usually constant and uncontrollablepressure and the fact that they require changing for different tools,may be disadvantageous. On the other hand, the double actingpressure-cylinders 180 act as ejectors and peel-off cylinders to providethe advantage of lesser bulk, being mounted outside the tool, andfurther allowing adjustment to the moment of force required in aparticular arrangement. Also, the cylinders need not be replaced fordifferent jobs. The piston rods 181 may be used as automatic ejectors.All operational parts previously located inside a tool employing springswill be on the side of the machine when the double acting cylinders areused, and tool simplification results.

Furthermore, the cylinders may perform various tasks. For instance twocylinders may be used as automatic ejectors when combined withadjustable registers 182 by means of actuating rods 183, while one ortwo further cylinders are used for forming shallow bottoms as indicatedby the actuation plate 185 in the lower part of the die part 186.

In further relation to FIGS. 15-17, to prevent the generation of shocksduring the vertical motions of die support 105 as well as affecting therelatively soft and sensible web material as acting upon the die partsor auxiliary equipment mounted thereon, and to prevent such shocks frombeing reflected into the unit 101 and from interfering with the smoothoperation of the machine and its drive, a weight composition or shockabsorbing system has been provided which has at least one power-storageelement that reaches below the lower die support 105. This weightcompensating device comprises at least one compressed fluid cylinder,preferably four compressed air cylinders 126 reaching below the fourcorner areas of lower die support 105 which are connected in parallel toa compressed air source that may be set for controlled supply or removaland measurement of the pressure to the desired pressurization by meansof apparatus. Compressed air cylinders 126 together with the pressurizedair source provide a power storage, braking in a definite mannerdetermined by the selected pressure in source, the downward motion ofdie support 105 while supporting its upward motion, the transmission ofdamaging shocks thus being prevented. As shown in FIG. 16, the weightcompensation device may instead be provided with hydraulic cylinders 129connected to a hydraulic pressure source container 130 operating inconcert with an air cushion. Hydraulic pressure container 130 is alsoprovided with an apparatus 128 for selectively setting the pressure onthe shock absorbing cushion. Usually there are only two hydrauliccylinders 129 below the lower die support 105, in diagonal arrangementas indicated in FIG. 18. However, four such cylinders may be provided.It is also conceivable that only one hydraulic or pneumatic cylinder beused, which might be mounted centrally below the lower die support. Asshown by FIGS. 15 and 17, the piston rods of the hydraulic or pneumaticcylinders (126,129 respectively) will only engage the lower side of thelower die support 105. One may therefore readily also operate withoutany weight compensating device by removing the pressures in sources 127or 130. Also, the pressure in the said sources may be selected so lowthat there will be some braking and damping action, but that the upwardmotion of die support 105 will be faster than that of the piston rods sothat the upward motion of die support 105 for the purpose of die closingwill not be affected by the shock absorbing or damping cylinders. Apressure valve allows operating the apparatus almost weightlessly, thatis, for constant pressure applied to the pistons of the compensatingcylinder, the same force for the same weight will always be obtained.

As further shown by FIG. 15, a central control device 170 is provided,to which is connected via line 172 a heat-radiation temperaturemeasuring element 171 mounted at dwell station 5. As shown by line 173,which is provided with an arrow, the drive motor (not shown) of gearunit 101 is controlled by the central control device 170. The latteralso controls via line 175 the drive device 174 for the adjustment ofthe second cooling roller 160, as indicated by double arrow 162. Itfurther controls via line 176 the tempering device 177 for the coolingmedium. This tempering device 177 is connected in known manner via lines178a, 178b and 178c with the interiors of cooling rollers 159 and 160and with free-running cooling roller 161. The tempering device 177 maybe constructed and operated in conventional manner in such fashion thatrollers 159, 160 and 161 may be maintained at different surfacetemperatures. Lastly, the central control device 170 also preferablycontrols the speeds of the drive means and the supply means for plasticextruder 156, neither of which is shown, as indicated by the line 179with arrow.

The desired normal operating conditions and the desired normalprocessing surface temperature of web I are set at the central controldevice 170. As soon as the temperature measurement element 171 senses asurface temperature on web I that exceeds the range of the processingtemperature, central control device 170 by means of drive system 174causes a leftward displacement of the cooling roller 160 in FIG. 15, sothat the contact area of web I with cooling rollers 159 and 160 will beincreased. If cooling roller 160 during this motion reaches its left-endlimit position, the displacement drive device 174 emits a feedbacksignal to the central control device 170. The latter then automaticallycauses the temperature of the cooling medium in the tempering device 177to be lowered for at least one of rollers 159, 160 and 161, for exampleroller 161, so as to increase the web cooling. However the temperatureof the cooling medium in all three rollers may also be decreasedsimultaneously.

If during such control of the cooling medium temperature a lowerpredetermined limit of temperature is reached, the tempering apparatus177 emits a feedback signal to the central control device 170, whichthen regulates the drive for the cam and gear unit 101 via line 173 andthe drive and supply for extruder 156 via line 179 towards greatermaterial transmission and operational speed of the apparatus. If thematerial of web I so allows, the central control device may further beso adjusted as to decrease the heat output at extruder 156 via line 179for such a case. If as a result of such control the surface temperatureof web I determined by measuring element 171 again decreases, thecontrol sequences indicated will be reversed in opposite sense by thecentral control device 170, that is, first the ordinary regulation oftemperature at extruder 156 and speed of operation at gear unit 101 willbe reinstituted, and thereafter the ordinary, preselected controlconditions at tempering device 177. If then the surface temperature ofweb I still remains below the preselected value, drive device 174 fordisplacing roller 160 will be activated in order to move the roller 160to the right in FIG. 15 and thereby decrease the contact area betweenweb I and rollers 159 and 160 and lower the cooling rate.

If the surface temperature of web I determined by measuring element 171falls below the selected value, then the central control device firstactuates drive 174 to displace roller 160 until either the desiredtemperature has been obtained or roller 160 reaches the right-end limitposition in FIG. 15. If the latter is the case, drive device 174 emits afeedback signal via line 175 to the central control device 170. Thelatter then regulates the tempering device 177 in order to raise thetemperature of the cooling medium for at least one of the rollers, sayroller 160, or for all three 159, 160 and 161. If this regulation isinsufficient, or if an upper temperature limit of the cooling medium isreached, tempering device 177 will emit a feedback signal via line 176to the central control device 170. If in that case the surfacetemperature of web I determined by the measuring element 171 is stilltoo low then the central control device 170 will cause the drive for camand gear unit 101 and that of the supply mechanism of the extruder 156to operate at a lower rate, so that the heating equipment of extruder156 will be more effective with respect to the material output, or elsethe central control device 170 causes an increase in heat output atextruder 156 via line 179 (if the plastic used allows).

If by these means the temperature of web I is raised into the desiredtemperature range, then the central control device 170 will firstregulate the operating conditions at extruder 156 and at the cam andgear unit 101 so as to revert to the desired normal value. If thetemperature of web I still remains at the desired level or is above it,then the central control device 170 will act upon tempering device 177in order to adjust to the preselected, normal temperature conditions ofthe cooling medium. Once the latter have been restored, the centralcontrol device will activate drive device 174 in order to displace theroller 160 so as to compensate for surface temperature fluctuations onweb I.

FIGS. 18-23 show a thermal forming machine provided with a lower diesupport 105 and an upper die support 106 hereinafter called the 2ndsupport, which are moved out of phase with respect to each othervertically along guiding columns 107 by a lifter lever 109 and lift rods111 and 112. This motion is effected by a drive system similar to thatof FIGS. 15-17 moving a link rod 110 in the direction of the doublearrow 110a to and fro and thereby inducing lifter lever 109 to oscillateabout axis 121. FIG. 18 shows the thermal forming machine when the diesor tools are in the open position, with lower support 105 at the lowestposition, and the 2nd support 106 in highest position. The up-and-downmotions of the lower die support 105 are damped by weight-compensator129, so that sudden shocks are avoided.

For the open position of the tools or dies shown in FIG. 18, the web ofthermoplastic material I, which is at the forming temperature, isconveyed in one operational step E in the direction of arrow D by aconveying system (not shown) that may be similar to that in FIG. 15.

A cooled thermal die 201 carrying lower precooling tools 231 and 233 ismounted on support 105; these two are connected to a conventionalcooling system (not shown) which may be a source of cooling fluidconnected to passages in the die or the tools.

Article shaping male form elements 221 project downwardly from the upperor 2nd die support 106. These forms may be mounted by being insertedfrom above into suitable apertures in thermal die 201. A clamping andstripping frame 222 is associated with thermal die 201 and positioned tobe moved onto web I from above. Frame 222 in operation is movable upwardagainst the action of prestressed compression springs 223 toward thelower side of a support plate 224, openings 225 permitting passage ofthe frame 222 above forms 221.

Further precooling tools referred to as precooling countertools 232 and234 are suspended from the 2nd support by means of support plates 236,and these tools in operation may be moved upward against the action ofthe prestressed compression springs 235 as far as the lower side of thesupport plates 236 on upper die support 106.

The pair of tool assemblies comprising precooling tool 231 andprecooling countertool 232 makes up the first precooling stage andcontains circular recesses 237 each having a diameter d₁ which, as shownin FIG. 19, results in defining circular areas 241 in web I that arekept free from precooling and are appreciably of larger diameter thanthe definitively shaped regions of thermal die 201.

The pair of tools comprising precooling tool 233 andprecooling-countertool 234 forms the second precooling stage andcontains circular recesses 238 in an arrangement similar to the firststage and of diameter d₂ appreciably smaller than d₁ but preservingcircular areas 242 in web I that are free from precooling and stillappreciably larger than the areas in web I to be thermally shaped.

The bottom face of frame 222 together with the upper face of thermalforming die 201 forms the third cooling stage for the residual materialin the web. This third cooling stage is substantially concurrent withthe thermal forming stage. Frame 222 is a plate provided with apertures225 for passage of the upper shaping forms 221 and the lower end ofpassages 225 are countersunk at 226 to cooperate with an annular, upwardprojecting die rib projection 203 adapted to form the rim 243 (FIG. 19)of the shaped article. The actual cup-like shaped article 244 is formedin the web by the descending forms 221 entering the correspondinglyshaped female form recesses in the lower die support and drawing the webmaterial to the desired shape.

Each length of the advance E of the web is equal to the length of thesuccessive stages of thermal die 201 in the same direction as regardsthe precooling tools 231, 233 and the precooling-countertools 232 and234.

When the lower die support 105 is lifted and the 2nd support is loweredin operation, the precooling tools 231 and 233 as well as the face ofthermal die 201 will be applied from below against web I, while theprecooling countertools 232 and 234 as well as frame 222 are loweredfrom above against web I. When further bringing together die support 105and the second support 106, springs 235 and 223 will become stressed, sothat the precooling tools 231 and 233 as well as the precoolingcountertools 232 and 234 will be urged under predetermined pressuresagainst the surfaces of web I. In the process, the above described areawise precooling of web I occurs simultaneously in both the first andsecond precooling stages. Simultaneously, there also takes place, duringthe thermal shaping process in the non-precooled areas of web I due tothe cooperation of thermal die 201 with frame 222 and forms 221, coolingin the third stage.

The apparatus after completion the shaping stroke is then moved backinto the open position of FIG. 18. The shaped articles in the web arelifted from the recesses 202 during this motion and web I is thenadvanced by one forward step a distance E in the sense of arrow D. Inthis manner, a new web section reaches the first precooling stage, theprecooled section from the first stage reaches the second precoolingstage, and the section from the second precooling stage reaches thecombined thermal shaping and third cooling stage. The recesses 237 ofthe first pre-forming stage, the recesses 238 of the second pre-formingstage and forming recesses 202 are so arranged and the web movement issuch that the non-precooled web areas 241 and the non-precooled webareas 242 of the second precooling stage respectively arrive inalignment with the recesses 238 and the shaping recesses 202. The lengthof each of the foregoing stages S₁, S₂ and S₃ is preferably equal to thedistance E.

Thus, each time the upper and lower die supports are brought toward eachother by rocking of lever 109, assuming that a length of heated web Iequal to three times the distance E is disposed between the tools, atfirst stage S₁ the section of the web pressed between tools 231 and 232is precooled except at areas 241 of FIG. 19; at second stage S₂ thesection of the web pressed between tools 234 and 235 is furtherprecooled except at areas 242 of FIG. 19, and at stage S₃ the articlesare thermally formed in the stabilized web by the action of projectingforms 221 entering recesses forms 202 and at the same time the websurfaces around the formed areas 243, 244 of FIG. 19 are further cooledby engagement of the opposite surfaces of the web with surfaces of die201 and frame 222. Each time the dies are separated, there is anintermittent advance of the web I for the distance E before the nextcooling and shaping stroke.

Since the upper tools 232 and 234 and the frame 222 are separatelyresiliently mounted on the upper die support their engagement pressureswith the web I are substantially uniform and resiliently applied andmaintained. When projecting forms 221 are performing the shapingoperation they are acting upon a web section in stage S₃ that isresiliently gripped and held flat between plate 222 and the lower die,so that smooth accurate shaping is effected. When the dies separate andforms 221 move upwardly frame 222 acts a stripper plate to help separatethe web from the shaping forms.

Somewhat modified tools or dies are illustrated as mounted on the lowertool support 105 and on the 2nd support 106 in the example of FIGS.20-23. All parts similar to those of FIGS. 18 and 19 have the samereference numerals. The recesses 255 in the precooling tool 251 nolonger are surrounded by cooling fields, but rather bycooling-and-shaping fins 256 cooperating with similarcooling-and-shaping fins 257 of the associated precooling countertool252. Fins 256 and 257 are peripherally continuous and although shown asrectangular may be any outline. The fins have countersunk mating regionsaround their peripheries. In this manner, grid-like ribs 245 are formedin web I at the first precooling stage, while the intervening andrectangular or roughly square areas 246 of the example shown remainuncooled. Precooling tool 253 and precooling countertool 254 in thesecond stage are provided with recesses 258 at the second precoolingstage, and these recesses are surrounded with oppositely contouredprecooling-and-shaping fins 259. In this manner, there is formed withinribs 245 a second oppositely shaped rib arrangement 247 surroundinguncooled areas 248 in FIGS. 22 and 23.

Lower thermal die 211 in the third stage of FIG. 20 is also modified atits upper face. Shaping die ribs 203 at each recess are providedtherearound with additional external ring-like forming bulges which maybe square with rounded-off corners 213 with grooves 214 (see FIG. 21)for receiving the ribs 247 shaped into web I. As shown in FIG. 21, thecooling and stripper frame 222a may be so constructed that it penetratesgrooves 214 so that the open side of the ribs 247 is thereby formed intoweb I. There are inclined forming surfaces 215 extending from theperipheral corners 213 to the shaping ribs 203, and these are matched bycorresponding countershaping areas 227 on the support 227 for shapingforms 221, as shown in FIG. 21.

This structure of the thermal die (FIGS. 22, 23) allows shaping awavelike rib structure 250 surrounding each shaped article area 249during the precooling stages and the thermal forming stage in theresidual web material, so that the residual material is subjected to amore intense cooling and desirably becomes a stiffened, framelikestructure which may be efficiently transported to and accuratelycentered in an adjoining stamping station.

In FIGS. 24 and 25 the apparatus consists of two units, namely a webmanufacturing unit 301 and a web processing unit 302. The formercomprises an extruder 311, which for example may be a worm extruder fedat its hopper 312 with fine, preferably granulated thermoplastics. Aweb-forming nozzle 313 at the extruder outlet receives the thermoplasticwhich has been softened by the heat and pressure applied in extruder 311and produces continuously a web 314 that is essentially at the extrusiontemperature when entering unit 302.

The web manufacturing unit 301 shown in its simplest constructional formin FIG. 24 may be additionally provided with extruders for differentkinds of thermoplastics also fed to nozzle 313 and connected to the neck315 mounted between extruder 311 and nozzle 313 as previously describedherein. A web 314 may be manufactured in this manner that consists oftwo or more layers of different thermoplastics or of differentlypretreated materials, for example differently dyed. One may also make aweb in such a manner that is coated on one or both surfaces with a thinplastic, for example anti-electrostatic in nature. One may also coat theweb with one or two surface layers of a material different from that ofthe main web, for example using impact-proof polystyrene for the webmaterial proper while one or both surfaces will be coated with apolycarbonate-based plastic.

The web manufactured by the unit 301 may be of relatively largethickness within the scope of the invention, for instance 3mm or more.This however does not exclude the feasibility of manufacturing andprocessing thinner webs, for instance from 0.5 to 2.0mm thick, by meansof the process and apparatus shown.

The web 314 delivered by unit 301 reaches a stabilizing-and-coolingdevice 322 mounted at the inlet of web processing unit 302 while stillessentially at the extrusion temperature. The distance between nozzle313 and the inlet to the stabilizing and cooling device 322 may beadjustably adapted to the particular requirements, for example theentire web processing unit 302 being movable by means of wheels orrollers 321.

Stabilizing and cooling device 322 may be provided with three coolingrollers 323a, 323b and 323c. As indicated in dashed lines, coolingrollers 323b and 323c may be adjusted transversely of the conveyingmovement of the web 314, in order to vary the looping angle and areasthat web 314 passes in heat conducting contact over the cooling rollers.However, as in the earlier embodiments, the stabilizing and coolingdevice 322 cools only a thin outer range of web 314, and stiffens theweb only slightly, while the material inside these surfaces ofstabilized web 314 essentially remains at the extrusion temperature andin the plastic state.

Web 314 passes from the stabilizing and cooling device 322 to equipment324 which feeds the web to the thermal shaping device, vertically andintermittently from top to bottom, and consists essentially of acompensating roller 325 and a gripper system 326 which is suitablycooled and intermittently moved up and down between the upper positionshown in full lines the lower one in dashed lines.

The gripper system 326 may be such that it engages web 314 only alongstrip like elements on gripping rails to minimize surface contact. It isso positioned with respect to the thermal shaping device that thoseparts of web 314 engaged by the strip-like elements and hence cooled bythem are in the residual web 314a, that is, they lie between the webareas that are to be shaped by the thermal forming device. Theillustrated gripper system consists of two parts which receive the web314 between them. They are pressed against each other to grip the webwhen the gripper system moves downward, while during the upward motionthey are held spaced apart and hence do not touch or move web 314.

The compensating roller 325 and the gripper system 326 are synchronouslycontrolled for the up-and-down motions, the upward motion of thecompensating roller taking place continuously at half the incoming speedof web 314 which is also continuous. The downward motion of thecompensating roller occurs simultaneously with that of the grippersystem and in steps that correspond to the length of the web sectionwhich is to be processed during each interval at the thermal formingstation 330.

The thermal shaping station 330 is preferably mounted underneath grippersystem 326, so that it receives the web in intermittently advancedvertical steps and web feed is aided by gravity. This thermal shapingstation 330 is characterized by a system of dies or tools and theiraccessories, wherein the die to which the web is to be fed is locatedfor horizontal displacement opposite the web. The thermal shapingstation 330 further comprises means for separating the shaped articlesfrom the web.

As shown in FIGS. 24 and 25, thermal shaping station 330 comprises a diesupport 331 which may rotate about a horizontal axis, and it containsfour spaced independent tools 332 that are 90° apart from each other.For the sake of simplicity, the drawing shows only single tools 332, butpractically these will be multiple tools in order to produce a pluralityof shaped articles during each single sequence of operation at thethermal shaping station.

As shown in FIG. 25, each of the four tools 332 is recessed to receive aforming element and is radially slidably supported in the die support331 so as to be displaceable against the action of springs 333. Therotational axis of support 331 is indicated at 336. Devices (not shown)may be mounted at the center of the die support 331 which will retaindie 332 in a retracted position, for a predetermined time, for exampleuntil the shaped article is ejected, at least until die support 331 hasreached its initial horizontal position. This avoids pushing back theshaped articles toward the residual web after termination of the shapingand stamping process.

In the rest position shown in FIG. 25, each of the recessed form tools332 projects from the particular side face of die support 331 by thedistance its rim 334 surrounding the tool recess. Two guide bores 335are provided in the die support 331 at each side face of the particulardie 332 by means of which die support 331 in its motion toward the webwill slide upon centering or pilot rods 328 mounted above the machineframe 327 of the web processing unit 302. The horizontal pivotcontaining axis 336 of die support 331 is parallel to the verticallydisposed web 314 and mounted on a guiding frame 337. Frame 337 ishorizontally slidably mounted by two guide rods 338 connected to a crankassembly 339 that operates to effect a horizontal to-and-fro motion ofdie support 331 with respect to the web. Alternately, guide rods 338 mayalso be moved to and fro as by correspondingly controlled pressurecylinders. Both guide rods 338 are slidably supported along theirhorizontal longitudinal axes, which are at right angles to the surfaceof web 314, in a slide guide member 329 mounted on the machine frame327, and member 329 also supporting the centering rods 328 which areparallel to guide rods 338.

The accessories of the tools and the separation system are mounted onthe guide member 329, and one structure is provided in common foroperation with each of all four tools 332 as they act on the web. Aforming system 340 is mounted on guide member 329 to that end,consisting of a projecting form element 341 shaped correspondingly torecessed tool 332, or a forming system adapted to multiple tools and apressure cylinder 342 is connected for selectively horizontallydisplacing the form element 341 into the oppositely positioned toolrecess.

A holding and stripper assembly 343 composed of three plates andoperating on web 314 is mounted on the centering rods 328. Assembly 343comprises a rear stop plate 344, a center plate 345 and a front plate346 facing the support 331. The rear stop plate 344 is mounted on guidemember 329, whereas the center and front plates 345 and 346 are slidablealong the centering rods 328. The three plates 344, 345 and 346 arebiased spaced apart by compression springs 347 disposed between rearstop plate 344 and center plate 345 and by compression springs 348 alsomounted on centering rods 328 and disposed between the center and frontplates 345 and 346. However these plates will be pushed toward eachother against the action of springs 347 and 348 when the die support 331approaches and engages in operation, and thereby be strongly compressedwhile resiliently clamping web 314 under pressure, so that the diesupport in moving over centering rods 328 will abut the adjacent endface of tool 332 against the front plate 346. The center and frontstretching frame plates 345 and 346 are provided with oppositely locatedtensioning rails 349 engaging web 314 in operation.

The front plate 346 is provided with an aperture 351 for the formationof a separation system 350, and aperture 351 receives with play theprojecting opening rim 334 of advancing tool 332. The rear peripheralrim 352 of this opening 351 acts as a cutting edge. The counter-elementcooperating with this cutting edge 352 is a stamping knife 353 on rearstop plate 344 into which the shaped part of the web is displaced byform element 341.

At the end of the article forming operation wherein the tool 332 ishorizontally engaged with the assembly 343 and form 341 is advanced todraw the web material into the recess of tool 332, the die support 331is moved away from assembly 343 and at the same time form 341 isretracted to the FIG. 25 position, leaving the formed article, orarticles, in the recessed tool 332. The residual web is then moveddownward.

A removal device 360 for the residual web 314a is mounted below theactual thermal shaping device 330, and in the example shown thisconsists of an intermittently driven removal roller 361 and counterroller 362. The residual web is led from this removal system 360 to thesize-reducing device 370 shown schematically in FIG. 24 and mounted onthe web processing unit 302. The residual web may thus be reconvertedinto granular material in unit 370 and then immediately fed back to theextruder hopper 312 in the system as indicated by line 371. As shown byarrow 372, the feedback material may be mixed with fresh material in thehopper. However, one may also store the granulated material and make useof it only later.

As shown in FIG. 24, devices 380 for catching and removing shapedarticles ejected from tools 332 when they reach the position 180° fromthe forming position are mounted at the side of die support 331 oppositeweb 314. The ejection of the shaped articles is effected by vacuum andcompressed air lines 381 opening into the cavities in dies 332, andthese lines are connected via valves controlled from the central machinecontrol to suitable vacuum and compressed air sources. The periodicrotation of die support 331 and of removal roller 361 is preferablyeffected by an electrical motor 382 periodically energized from thecentral machine control. The drive of crank drive is effected by anelectrical motor 383, which may also operate periodically and becontrolled from the central machine control. Preferably however, acontinuously operating drive motor 383 will be used, and the centralcontrol for the continuously or periodically operating devices of theweb processing unit 302 will be connected to shaft 384 of the crankdrive at 339. By controlling the speed of drive motor 383, one mayregulate over a sufficiently wide range the operational rate or outputof the web processing unit 302 so as to adapt it to the output ofextruder 311 and nozzle 313. Further, extruder 311 may be controlled inknown manner with respect to its own output.

The operation of the foregoing system is as follows:

Web 314 issuing from nozzle 313 enters the stabilizing and coolingdevice 322. By proper setting of the cooling rollers 323b and 323c, thefirst processing step of the invention is executed, namely a stabilizingsurface temperature is provided for the hot plastic web 314 coming fromnozzle 313, which temperature is low enough to stabilize the surfaces ofthat web, so that the continuously incoming web may be intermittentlymoved through the thermal forming machine. Web 314 is fed continuouslyfrom the stabilizing and cooling device 322 to the compensating roller325, which converts continuous web motion to intermittent downwardvertical motion, the synchronism and the length of such intermittentmotion being determined by the central control system. The compensatingroller 325 is supported by the gripper system 326. When the thermalshaping device 331 is in the open position shown in FIG. 25 andtherefore with the plates of frame 343 biased to open condition bysprings 347 and 348, compensating roller 325 and the gripper system 326will be driven downward in the sense of the solid arrow 326a, both partsof the gripper system 326 being pressed toward each other to resilientlyclamp the web between them. The length of such discrete motion may beadjusted to the vertical length of the web section gripped by clampingribs 349 on frame 343, plus a minor length of web which is touched byupper and lower transverse ribs on gripper system 326. The compensatingroller 325 again moves from its lower position, showed in dash lines,towards its upper position in a loop forming function during thecontinuous feeding of web 314. The parts of the gripper system 326 willbe separated from one another and from web 314 after reaching the lowerposition and then moved back upward according to dashed arrow 326b intothe initial position.

Motor 383 also is switched ON by the central control system during thedownward web advance step. Thereby, the residual section of web in thethermal forming station is removed simultaneously with the feeding of anew section into the thermal forming station 330. Also, die support 331is rotated by 90° in the sense of arrow 331a, so that the next tool 332moved into position now faces a new section of web 314. The centralcontrol system may be so connected with shaft 384 of the crank drive 339that shortly after termination of the web advance step, crank drive 339will move the die support 331 into contact with the front plate 346. Therim 334 of die 332 will then extend into the aperture 351 of the frontplate 346. The thickness of latter inside the clamping rib 349 is equalto the height of the aperture rim 334, so that the front face of the die332 will lie in the plane of the rear area of the front plate 346 andwithin the clamping rib.

Springs 348 being considerably weaker than springs 347, the front frameplate 346 at first will be urged against the center plate 345 whileclamping web 314. At this moment, the central control system energizesthe pressure cylinder 342 of form element 341 for the initiation of theactual thermal forming process, so that the element 341 pushes thecentral region of the clamped area to be shaped of web 314 into thehollow space of die 332. Upon further rotation of crank drive 339, bothplates 345 and 346 will be advanced along rods 328, compressing springs347, until the center plate 345 abuts stop plate 344. During thismotion, first the front face of the stamping knife 353 will contact web314 which already has been subjected to shaping by form element 341.Subsequently the front face of the opening rim 334 presses the web inthe area surrounding the shaped article against the front face of thestamping knife 353, so that the space surrounding the latter is sealedat the side toward web 314. If form element 341 is being moved towardthe web at this time the pressure of compressed air generated in thesealed region together with the vacuum applied to supply lines 381 inthe die support 331 will combine with the forming action of the tool toeffect complete forming of the shaped articles in the web.

The mutual front-face bracing of die 332 and stamping knife 353 takesplace before the center plate 345 contacts stop plate 344. Therefore,during the further motion of die support 331 toward web 314 by crankdrive 339, die 332 will be displaced into the interior of die support331 against the action of springs 333, stamping knife 353 passing intorecess 351 of the front frame plate 346 and separating the shapingarticle from the web along the cutting edge 352. Despite suchseparation, the above described complete shaping process by the actionof the compressed air continues as long as die 332 and stamping knife353 mutually brace each other while clamping the rim of the shapedarticles, and also still during the first part of the horizontal returnmotion of the die support 331. The vacuum applied to the supply line 381in each case will remain in the state shown in FIG. 25 even after thereturn motion of die support 331.

Once the tool support 331 has been moved away from the web at least sofar that the bores 335 leave centering rods 328, and after the openingrim 334 of the die 332 has left the recess 331 of the front frame plate346, the next advance step for web 314 may be initiated by the centralcontrol system. As explained above, the die carrier 331 will be rotatedby 90° clockwise in FIG. 24, so that the previously upward pointing tool332 now will face web 314. The supply line 381 still remains connectedto the vacuum, so that the separated shaped article received by the tool332 remains in the tool after completion of the thermal formingoperation and will be cooled therein. After termination of the nextthermal forming operation when the die support 331 has been rotated by180° from the article forming position, the supply line 381 isdisconnected from the vacuum source and is connected thereafter to acompressed air source so that the cooled shaped article may be ejectedby air pressure from die 332 and transferred to the receiving andremoving device 380. Any suitable arrangement for selectively connectingthe different lines 381 to sources of vacuum and air pressure dependingon the rotated position of support 331 may be provided. In any eventvacuum is applied into the bottom of the cavity of the tool 332 facingthe web, and air pressure for ejecting the article is supplied into thebottom of the cavity but is 180° away from the forming position.

Modifications of the above may be undertaken. For instance the diesupport 331 might be carried during the described intermittent rotationby the machine frame 327, while the guide member 329 may be movedhorizontally to and fro together with the parts of the thermal shapingdevice and the separation system 350 mounted on it, by means of crankdrive 339.

If desired, the cooling period of the shaped articles 385 in the die 352may be increased by intermittently rotating the die carrier 331 in anopposite direction from that indicated by arrow 331a and by mounting thereceiving and removing device 380 for shaped articles 385 beneath diesupport 331. The shaped articles in such a case would be cooled for theadditional time of two consecutive thermal shaping operations.Conceivably, die support 331 may be provided with more than four tools332 and with correspondingly more angular tool operating positions. Onthe other hand, it is entirely conceivable that the die support 331 byequipped with fewer, for instance with two or three tools 332 ormultiple tools, and that there be fewer such angular positions.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

We claim:
 1. Apparatus for manufacturing thin-walled synthetic plastic articles which comprises extrusion means for forming a continuous hot plastic web of thermoplastic material at a predetermined high temperature, means for substantially immediately stabilizing said web to self supporting condition by cooling opposite surfaces of the web to provide therealong continuous outer supportive layers that are sufficiently deformable for shaping in subsequent shaping tool operation while the hot plastic material between said layers remains sufficiently plastic and fluid for redistribution between said layers during said tool operation, and means for advancing the stabilized web toward and into a thermal forming station in synchronism with shaping tools in said station adapted for forming articles in successive areas of said web during the period that said hot plastic material between the layers remains capable of redistribution between them.
 2. Apparatus as defined in claim 1, wherein means is provided for continuously moving said web through said stabilization means, and said cooling means comprises means in area contact with the continuously moving web surfaces for relatively rapid cooling of the web surfaces.
 3. Apparatus as defined in claim 2, wherein said means for cooling the web surfaces comprises a plurality of cooling rollers over which said hot plastic web is drawn in opposite surface contact, and means is provided for controlling the amount of heat exchange between said rollers and the web surfaces.
 4. Apparatus as defined in claim 3, wherein said means for controlling heat exchange comprises means for adjustably varying the areas of contact between said rollers and said web surfaces.
 5. Apparatus as defined in claim 4, wherein one of said cooling rollers rotates on a fixed axis and another of said rollers is selectively movable in an arc about said axis.
 6. Apparatus as defined in claim 4, wherein a first cooling roller is provided rotating about a fixed axis and second and third cooling rollers are provided at opposite sides of said first cooling roller, said second and third cooling rollers being adjustable in a direction perpendicular to a horizontal plane containing said axis.
 7. Apparatus as defined in claim 3, wherein said cooling rollers are adapted to be cooled by means of fluid cooling medium and wherein said controlling heat exchange comprises means for adjustably varying the temperature of said cooling medium.
 8. The apparatus defined in claim 1, including means defining a treatment station for treating the outer layers of said stabilized web for obtaining uniform temperature distribution across the outer surfaces of successive web areas prior to said tool operation.
 9. The apparatus defined in claim 9, wherein temperature distribution is effected by means providing proportional reflection of radiant heat from the hot plastic web.
 10. The apparatus defined in claim 8, including means whereby air at controlled temperature is circulated over the layer surfaces at said areas for effecting temperature distribution.
 11. Apparatus as defined in claim 8, wherein means is provided for converting continuous advance of said web through said stabilizing means into intermittent advance into and through said web surface treatment station whereby successive web areas are disposed for a predetermined period of said station.
 12. Apparatus as defined in claim 1, including means whereby said areas of said stabilized web are intermittently introduced in succession into said thermal forming station.
 13. Apparatus as defined in claim 12, wherein said shaping tool means comprises at least one contoured forming die surface against which one surface of the web is pressed, and means is provided acting on the other side of said web for forcing said web into contact with said one die surface.
 14. Apparatus as defined in claim 13, wherein said other surface of the web is engaged by a web stretching die element.
 15. Apparatus as defined in claim 13, wherein fluid pressure is applied to the other side of said web to urge the web into contact with said one die surface.
 16. Apparatus as defined in claim 1, characterized in that means synchronized with the shaping operation is provided for precooling the web prior to said shaping.
 17. Apparatus as defined in claim 16, characterized in that said precooling means comprises cooled tools having recessed areas that during precooling do not contact the surface of the web at the areas to be shaped into articles.
 18. Apparatus as defined in claim 16, characterized in that the precooling means comprises tools of coacting form mounted on opposite sides of the web.
 19. Apparatus as defined in claim 17, characterized in that said precooling means is provided with surfaces at those parts that touch the surface of the web for forming into the web a framelike structure outside the areas to be shaped.
 20. Apparatus as defined in claim 16, characterized in that precooling is effected in a plurality of correlated successive stages in each of which a web section of predetermined length is successively disposed.
 21. Apparatus as defined in claim 20, characterized in that recessed areas of different size are provided in the consecutive precooling stages such that the non-cooled areas are smaller in the successive stages.
 22. Apparatus as defined in claim 16, where means is provided whereby a thermal die is moved to and from the web by a support and means is provided whereby the web is moved at right angles to the direction of motion of the thermal die through the latter's operating range and intermittently in steps adapted to the movement of the thermal die, characterized in that at least one precooling means correlated with respect to size and recessed areas in the thermal die is mounted on the support in the path of the web upstream of the thermal die and for simultaneous motion with said thermal die.
 23. Apparatus as defined in claim 22, where accessories such as forming elements and counter dies relating to the thermal die are mounted on a second support moved out of phase with respect to said first support, characterized in that at least one second precooling means is mounted on the second support, the structure of which corresponds essentially to that of the first precooling means, and in that the second precooling means and the first precooling means are constructed and arranged for clamping the web with firm bilateral pressure when the thermal die is closed.
 24. Apparatus as defined in claim 22, characterized in that means is provided whereby the first precooling means and/or the second precooling means may be retracted against the action of compression springs in the direction of said supports.
 25. Apparatus as defined in claim 16, characterized in that pneumatic or hydraulic cylinders are provided for supporting both of said precooling means under predetermined pressure.
 26. Apparatus as defined in claim 23, characterized in that positive and negative shaping elements are provided on at least one cooperating pair of precooling means for the formation of a framelike structure in the cooled stabilized web.
 27. Apparatus as defined in claim 1, wherein means is provided for subsequently stamping the formed articles out of said web.
 28. Apparatus for manufacturing thin-walled synthetic plastic articles which comprises means including extrusion means for forming a continuous plastic web of thermoplastic material at a selected high temperature and means for substantially immediately stabilizing said web to self supporting condition by cooling opposite surfaces of the web to provide therealong continuous outer supportive layers that are sufficiently deformable for shaping in subsequent shaping tool operation while the hot plastic material between said layers remains sufficiently plastic and fluid for redistribution between said layers during said tool operation, and means for advancing the stabilized web toward and into a thermal forming station wherein successive areas of the web are subjected to the action of shaping tool means, said web advance being effected at such speed and in such timed relation to operation of the shaping tool means and in such correspondence with the web extrusion temperature that said stabilized web arrives at said thermal forming station while it retains sufficient heat in its inner core portion to partially reheat its cooled surface layers by heat conduction from the inner core portion outwardly during transport from said stabilizing means to said thermal forming station so that said layers are elastically deformable for improved shaping. 